Symptoms of zinc deficiency of almond Written by Franz Niederholzer, UCCE Advisor, Colusa and Sutter/Yuba Counties Bloom is the most important time of the year for adequate boron (B) and zinc (Zn) levels in almonds.  Zinc is essential to many processes such as cell division, protein synthesis and auxin synthesis in growing points (flowers and shoots), and bloom is the time of the most growing points in a tree.  Boron is essential for cell wall synthesis and division. Boron fertilization has improved fruit or nut set compared to deficient plants in many crops, but only if applied in time to get B into buds at bloom.  Both Zn and B can be absorbed into leaves and translocated within almond trees. Check leaf symptoms, summer leaf analysis or hull analysis results to see if Zn and/or B fertilization is needed.  Zinc deficiency produces “little leaf” symptoms (see photo below), with trees showing summer leaf levels of 15 ppm Zn or less considered deficient.  Trees with hull B levels below 80 ppm B at harvest are thought to be deficient, but almond yield may benefit from B application if hull levels are below 120 ppm B.  Do not fertilizer with B if hull levels are 200 ppm B or greater, as excessive B is toxic to plants. A fall foliar nutrient spray is a cost effective way to get Zn or B into buds for the following year’s bloom.  The return on investment for a fall B spray can be significant.  Yield increases of 200-400 kernel pounds per acre have been measured from a foliar nutrient application the previous fall at Nickels Soil Lab of 0.6 lbs. of actual B (the equivalent of 3 lbs. Solubor®/acre applied in 400 gallons/acre). Fall Zn sprays should increase leaf Zn the following year and eliminate Zn